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Saturday, July 14, 2012

Why we still wear pants

Peter
Turchin recently published a series of blogs (part 1 and part 2) addressing the
question of why westerners wear pants.
It's a story I'd heard before years ago in a comparative Indo-European
studies course, but not from an expressly evolutionary perspective and not with
Peter's flare. It's a good story,
particularly for introducing cultural evolution, and I don't want to spoil it
for those who haven't heard it before.
Nevertheless, not much about this post will make sense if I don't at
least mention that wearing pants came about whenever riding horses became an
important part of warfare.

As
much as I like the story, I made what I thought was a somewhat innocuous
comment saying that I would like to see a follow up series of blogs that
explored why we still wear pants. After
all, very few people ride horses and, aside from some special exceptions, horse
cavalry became obsolete in World War 1.
However, not only has the wearing of pants continued, it has spread,
both to societies we've come into contact with and to women within our own
society. This spread has happened
without any obvious adaptive advantage.
Moreover, this persistence and spread has occurred despite available
alternatives and social movements, such as the androgynous movement of the 1980s,
that attempted, and failed, to change these established practices.

Peter's
response to this question, while not exactly surprising, was surprisingly
dismissive. His position is that there
is no need to explain when cultural traits fail to change. For him, the lack of change is the null
hypothesis. In his own words:

The
null model is dp/dt = 0, where p is the frequency of the trait, and dp/dt it’s
(sic) rate of change. If there is change, then dp/dt = c, or dp/dt = cp,
depending on the details of how the trait changes. In any case, the greater the
rate parameter, c, the faster the trait will change. So if c is high enough you
will have yearly changes of fashion, if c is small enough, then it will take
decades or even centuries.

The
failure of something to change, in Peter's view as I understand it, can simply
be dismissed as normal inheritance. In
the absence of variation and/or in the absence of selection pressure to change,
we simply go on as we've always done.

I
object to this position on a number of fronts.
To begin, it appears to be an assumption, not an empirically established
fact. Moreover, all these equations
really establish is that some traits change faster than others, hardly a
startling revelation. What they fail
utterly to do is account for why some traits change faster than others. The salient question, for me, is why dp/dt
should ever be zero, or even near zero.

It
is, of course, entirely plausible that Peter is right, that the failure of this particular trait to change might be due to simple inertial processes. However, this is far from the only
possibility. We need only look to
biological systems to see why this is so.
Robustness, the propensity of a system to continue functioning in the
face of perturbation, is a general property of complex, evolved systems. The structure of DNA and the genetic code are
robust to mutations. Proteins similarly
tend to perform their functions even with amino acid substitutions. This robustness is evident all the way up the
hierarchy of biological complexity. Even
developmental systems are robust to changes in metabolic pathways.

I
see no logical reason to assume this general property of biological systems, a
property that is an adaptation in its own right, should somehow no longer hold
true once the level of complexity moves outside the skin of the individual
organism. Moreover, if evolutionary
approaches to understanding human culture are to meet their full potential,
they must grapple with practical problems in the current world, many of which
represent historical patterns from which groups seem almost incapable of
escaping. For instance, Nisbett andCohen have traced modern rates of male violence in the southern United States
to Celtic herding cultures, an ancestral pattern that has persisted long after
herding faded out as a way of life.
Similarly, Robert Putnam has traced failures of democratic institutions
in southern Italy to patterns of social capital building that go back 500
years.

Treating
the persistence of these problems as nothing more than null hypotheses
drastically reduces the chances of finding real solutions. Aside from blinding ourselves to the root
causes of recalcitrance, robustness paradoxically makes evolvability possible. A handful of textbook examples
notwithstanding, it is rare for a single mutation in biological systems to be
adaptive. Most often, adaptations arise
from a series of mutations. Fragile
systems, however, are relatively incapable of building pools of useful
variation since any slight change is likely to lead to suboptimal
performance. Robust systems, by
contrast, tend to build up pools of variation, some combination of which may
prove adaptive when new niches present themselves or existing environmental
conditions change.

As
for the question that ultimately motivated this post, I have no idea why we are
still wearing pants. If I were to hazard
a guess, I would say that once pants became associated with warrior castes they
acquired protection by virtue of prestige bias.
This in itself, though, might not have been enough to ensure the
practice persisted. More likely, the
wearing of pants started to get tied to concepts in addition to warrior
attire. For instance, pants became associated
with markers of gender identity, group heritage, etc. In other words, it became connected to many
other cultural constructs in intricate webs not unlike the way genes often have
pleiotropic effects in gene networks. If
so, then wearing pants could become difficult to change even if there were
compelling reasons to do so.

Sure,
this is all purely conjecture at this point.
However, it hopefully goes some ways toward demonstrating that lack of
change is a worthy subject for evolutionary study.

1 comment:

the use of pants is still spreading, among women in western countries and among the general population in non-western countries. It's still a symbol of status and of belonging to a certain economic/business class. Look at the lyrics to Fela Kuti's "Gentleman" (https://www.youtube.com/watch?v=snIV_-IECsM) to see how there is nothing static about the use of pants around the world.